Temperature measurment

ABSTRACT

A device for measuring temperature in which an inductance coil surrounds each arm of a glass manometer containing a liquid such as mercury acted on by a temperature expansive liquid such as ethyl alcohol. Each inductance coil forms part of an oscillatory circuit and the outputs of the two oscillatory circuits are compared in a beat frequency mixer to give a digital representation of the temperature.

United States Patent 1191 Young 1 51 Jan. 2, 1973 s41 TEMPERATUREMEASURMENT 2,097,100 10/1937 Linsell ..73/362 R ux 2,491,486 12/1949Ewen .....73/362 R UX [76] Invent gg l f 'g s gr' 'g i m 2,721,26710/1955 Collins ..73/362 R x [22] Filed: Oct. 2, 1970 PrimaryExaminer-Louis R. Prince 21 A L No: 77 688 Assistant Examiner-FrederickShoon I 1 pp Attorney-Holman & Stern [30] Foreign Application PriorityData 57 ABSTRACT Oct. 3, Great Britain A devi e for measuringtemperature in an inductance coil surrounds each arm of a glass manome-[22] {18.82. ..73/362 R, 73/368, 331/66 ter containing a liquid Such asmercury acted on by a l 'f "Golk 5/18 3 5/30 temperature expansiveliquid such as ethyl alcohol. 1 o a 362 331/66 Each inductance coilforms part of an oscillatory circuit and the outputs of the twooscillatory circuits are [56] References cued compared in a beatfrequency mixer to give a digital UNITED STATES PATENTS representationof the temperature.

3,459,043 8/1969 Young ..73/362 R 1 Claim, 3 Drawing Figures OSCILLATORj-( I MIXER OSCILLATOR PATENTEDJAIZ m 3.707.873

TRANSDUCEHR- i 7 FIG 2 7 INPUT INPUT OUTPUT TEMPERATURE MEASURMENT Thisinvention relates to methods of and devices for measuring temperature.

According to one aspect of the present invention, there is provided amethod of measuring temperature, comprising comparing the difference inpositions of columns of liquid in the arms of a manometer caused by theaction of a temperature expansive fluid on the liquid, said arms beingsurrounded by inductance coils so that variation of the column heightaffects the inductance values, said comparison being effected bycomparing the inductances or variations therein of the inductance coils,and utilizing this inductance comparison to provide a measurement of thetemperature.

According to another aspect of the present invention, there is provideda device for measuring temperature, comprising a manometer containing aliquid arranged to be acted on by a temperature expansive fluid, aninductance coil surrounding each arm of the manometer and arranged sothat a change in position of the column of liquid in the arm due to achange in temperature causes a variation in the inductance of the coil,and means for comparing the inductances or variations therein of theinductance coils to provide a comparison of the difference in positionof the column of liquid in the arms and thereby to provide a measurementof the temperature.

Preferably each inductance coil forms part of an oscillatory circuit ofan oscillator and the output oscillations are compared so that thedifference frequency impulses provide a representation of thetemperature being measured.

An embodiment of the present invention will now be described, by way ofexample, with reference to the accompanying drawing, in which:

FIG. 1 is a schematic diagram of an embodiment of the present invention,

FIG. 2 is a circuit diagram of an oscillator which can advantageously beused in the embodiment of FIG. 1, and

FIG. 3 is a circuit diagramof a mixer which may be used in theembodiment of FIG. 1.

A device for measuring temperature comprises a glass manometer lcontaining a column 2 of mercury in each arm thereof and having a bulb 3connected to one arm 4, the other arm being open to the atmosphere. Thebulb 3 and the arm 4 to which the bulb 3 is connected are filled with atemperature expansive fluid, in this case ethyl alcohol. Around each arm4 and 5'of the manometer I is arranged an inductance coil 6' and 7,

respectively. Each coil 6 or 7 forms with a capacitor 8" or a resonantcircuit which forms part of an oscillator or 11, a co-axial cable l2'or13 connectingcapacitor 8 or 9 with the rest of the oscillator 10or 11-.

The two oscillators l0 and 11 are substantially identical and preferablyshare a dual transistor or are built up on an integrated circuitchip.The oscillator 11 is a Clapp-type oscillator (see FIG. 2) providing anoscillatory output on line 14 to a beat frequency mixer 15. Movement ofthe mercury along the axis of coil 7 causes variation in the inductanceof the coil and hence variation in the frequency of the output on line14'.

Oscillator 10 is similarly connected via the co-axial cable 12 and thecapacitor 8 to the inductance coil 6. The output of oscillator 10 istaken on line 16 to mixer 15, the output 1 7 of which provides a digitalrepresentation of the height variation of mercury in the arms 4 and 5,thus giving an indication of the temperature being measured.

FIG. 2 is a circuit diagram of a Clapp oscillator which may be used inthe embodiment of FIG. 1. The oscillatory circuit formed principally bycapacitor 9 and coil 7 is connected between collector and emitter of atransistor 18 and ground. The advantage of the Clapp type of circuit isthat the capacitance of the co-axial cable 13 has but a small effect onthe resonant frequency of the oscillator so that a substantial length ofcable may be used where necessary.

FIG. 3 is a circuit diagram of a beat frequency mixer which may be usedin the embodiment of FIG. 1 at 15. The outputs of oscillators l0 and 11are respectively fed to the inputs of two transistors 28 and 19 (whichmay be combined in a dual transistor), the output being taken from acommon base connection at 20.

If desired, the arm 5 of the manometer 1 which is not connected with thebulb 3 may be sealed off and the space above the mercury in that armevacuated or filled with an inert gas or with a small quantity of theexpansive fluid used in the bulb 3 which latter arrangement would, it isbelieved, increase the effective temperature range of the device as withthe inert gas.

In the place of ethyl alcohol, another expansive fluid may be employed,for example pentane or methyl alcohol. A liquid other than mercury maybe employed in the manometer e.g., liquid sodium or potassium. Suitabledielectric materials other than glass may be employed for the manometer.

Ina device for measuring temperature according to the present invention,the use of two oscillators to measure the difference in height betweencolumns of liquid in the arms of a manometer and the comparison of theoutput oscillations from the oscillator to give a difference frequencygives double the sensitivity of that obtained by using a single tubecontaining an expansive fluid and'comparing the single outputoscillation with a pre-fixed second oscillator, such an arrangementbeing described in my British Pat. specification No.

on by a temperature expansive fluid; an inductance coil surrounding eacharm of the manometer andarranged so that a change in position ofthecolumn of liquid in the arm due to a'change in temperature causes avariation in the inductance of the coil; a capacitor coupled to eachinductance coil to form therewith first and second resonant circuits;first and second Clapp-type oscillator means, each comprising atransistor; coaxial cable means for connecting said first and secondresona'nt circuits between the collector and emitter and ground of eachsaid transistor, respectively, whereby said first and second Clapp-typeoscillator means oscillate at a frequency determined by the variation ininductance of the inductance coil respectively associated therewith;beat frequency mixer means comprising a transistor pair having theirrespective collector-emitter paths coupled in parallel circuitarrangement to ground through a resistor, first and second inputs forsaid mixer means comprising the base of each transistor of the pair towhich the outputs of said first and second oscillator 5 means areconnected, and a mixer output coupled across said resistor, said mixeroutput defining a digital representation of the temperature beingmeasured.

1. A device for measuring temperature, comprising: a manometercontaining a liquid arranged to be acted on by a temperature expansivefluid; an inductance coil surrounding each arm of the manometer andarranged so that a change in position of the column of liquid in the armdue to a change in temperature causes a variation in the inductance ofthe coil; a capacitor coupled to each inductance coil to form therewithfirst and second resonant circuits; first and second Clapp-typeoscillator means, each comprising a transistor; coaxial cable means forconnecting said first and second resonant circuits between the collectorand emitter and ground of each said transistor, respectively, wherebysaid first and second Clapp-type oscillator means oscillate at afrequency determined by the variation in inductance of the inductancecoil respectively associated therewith; beat frequency mixer meanscomprising a transistor pair having their respective collector-emitterpaths coupled in parallel circuit arrangement to ground through aresistor, first and second inputs for said mixer means comprising thebase of each transistor of the pair to which the outputs of said firstand second oscillator means are connected, and a mixer output coupledacross said resistor, said mixer output defining a digitalrepresentation of the temperature being measured.